The present invention relates to a document reader configured to feed plural document sheets placed on a document tray to a document read position one by one and read image information from each of the document sheets. The present invention also relates to an image forming apparatus configured to form an image on a recording medium based on image information read from a document sheet by the document reader.
Recent years have seen a progressing development of document readers of the type adapted to read image information from document sheets at a predetermined image read position during feeding of the document sheets one by one, as disclosed in Japanese Laid-open Patent Application No. H07-095364.
Such a document reader defines therein a document feed path extending from the document tray, through the image read position, to the delivery tray. The document tray is capable of receiving plural document sheets as stacked thereon. The delivery tray receives the document sheets as stacked thereon after the reading of image information therefrom.
The light-receiving surface of an image reading device faces the image read position on the document feed path either directly or via a deflecting mirror. Each document sheet under feeding on the document feed path travels in the secondary scanning direction with respect to the light-receiving surface of the image reading device. While the length of the document sheet from the leading edge thereof to the trailing edge thereof in the document feed direction passes through the image read position, the image reading device reads image information from the entire image bearing side of the document sheet.
However, a conventional document reader cannot read image information continuously from a series of differently sized document sheets including, as mixed, an A3-size document sheet and a B5-size document sheet for example, though can read image information continuously from a series of single-sized document sheets placed on the document tray.
The conventional document reader has a document sensor disposed on the document feed path at a location intermediate the document tray and the image read position for detecting the presence and absence of a document sheet so that an occurrence of a document feed failure is detected based on a detection signal from the document sensor. The document reader stops operating upon an occurrence of a change in duration of detection by the document sensor, which is regarded as an occurrence of a document feed failure. For this reason, when a change in document sheet size occurs during successive feeding of plural document sheets, a change in duration of detection by the document sensor occurs, which causes the document reader to stop operating. Thus, it becomes impossible to feed document sheets.
There exists no conventional document reader configured to determine the length of a document sheet in the primary scanning direction during feeding of the document sheet, though there exists a document reader of the type configured to determine the length of a document sheet placed on the document tray in the document feed direction (the direction perpendicular to the primary scanning direction).
Accordingly, even if plural document sheets of different sizes are fed successively by the neglect of the detection signal from the document sensor, image information reading from the same range as the dimension of a maximum-size document sheet is performed with respect to a document sheet of a smaller size in the primary scanning direction. This means that unnecessary image information from outside the image region of the smaller-sized document sheet is also read and processed. As a result, such a conventional document reader has the problem that the demand for higher-speed image reading cannot be satisfied.
Also, an image forming apparatus for forming an image on a recording medium with use of image information read by such a document reader performs image formation based on such unnecessary image information. Further, the image forming apparatus forms an image on a recording medium of an unnecessarily large size relative to the image information. Thus, the image forming apparatus has the problem that the demand for higher-speed image formation and resources saving cannot be satisfied.
A feature of the present invention is to provide a document reader capable of determining the length of a document sheet in the primary scanning direction immediately after start feeding of the document sheet to avoid reading of unnecessary image information from outside the image region of a smaller-sized document sheet, thereby continuously reading image information from a series of differently sized document sheets including mixed document sheets of different sizes. Another feature of the present invention is to provide an image forming apparatus capable of image formation based on image information continuously read from a series of such differently sized document sheets without waste.